"Sister from another mister?" Ellen writes in the caption to the August 13 post.

Kelly retweeted Ellen's link, adding, "First family photo."

Ellen's character, Meredith Grey, was seemingly unaware of the DNA she shares with the new Grey Sloan Memorial surgeon when Season 10 left off — she only knew Maggie as Cristina's pick for the hospital's new head of cardio.

The half-sister reveal might be new information to us, but Grey's creator Shonda Rhimes tells TV Guidethat she and the other writers have waited years to pull the Maggie trigger.

"It's not a thing where we're going in and backdating," she explains. "It's literally always been layered into the storyline. We can literally go back and pull out moments of the show, and I'm excited to do so and point out where it was talked about. It's not going to be so hard to do."